Explanation:
One of the brightest galaxies in planet Earth's sky is similar in size
to our Milky
Way Galaxy: big, beautiful M81.
This grand spiral galaxy can be found toward the northern constellation of the Great
Bear
(Ursa Major).
This superbly
detailed view reveals M81's bright yellow nucleus, blue
spiral arms, and sweeping cosmic dust lanes with a scale comparable to
the
Milky Way.
Hinting at a disorderly past,
a remarkable dust lane actually runs straight through the
disk, to the left of the galactic center,
contrary to M81's
other prominent
spiral features.
The errant
dust lane may be the lingering result of
a close encounter between
M81 and its smaller companion galaxy, M82.
Scrutiny of variable stars in
M81 has yielded one of the best
determined
distances for an external galaxy -- 11.8 million light-years.